content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.observable;
  
  import io.reactivex.common.Disposable;
  import io.reactivex.common.annotations.NonNull;
  
  /**
   * Provides a mechanism for receiving push-based notifications.
   * <p>
   * After a SingleObserver calls a {@link Single}'s {@link Single#subscribe subscribe} method,
   * first the Single calls {@link #onSubscribe(Disposable)} with a {@link Disposable} that allows
   * cancelling the sequence at any time, then the
   * {@code Single} calls only one of the SingleObserver {@link #onSuccess} and {@link #onError} methods to provide
   * notifications.
   *
   * @see <a href="http://reactivex.io/documentation/observable.html">ReactiveX documentation: Observable</a>
   * @param <T>
   *          the type of item the SingleObserver expects to observe
   * @since 2.0
   */
  public interface SingleObserver<T> {
  
      /**
       * Provides the SingleObserver with the means of cancelling (disposing) the
       * connection (channel) with the Single in both
       * synchronous (from within {@code onSubscribe(Disposable)} itself) and asynchronous manner.
       * @param d the Disposable instance whose {@link Disposable#dispose()} can
       * be called anytime to cancel the connection
       * @since 2.0
       */
      void onSubscribe(@NonNull Disposable d);
  
      /**
       * Notifies the SingleObserver with a single item and that the {@link Single} has finished sending
       * push-based notifications.
       * <p>
       * The {@link Single} will not call this method if it calls {@link #onError}.
       *
       * @param t
       *          the item emitted by the Single
       */
      void onSuccess(@NonNull T t);
  
      /**
       * Notifies the SingleObserver that the {@link Single} has experienced an error condition.
       * <p>
       * If the {@link Single} calls this method, it will not thereafter call {@link #onSuccess}.
       *
       * @param e
       *          the exception encountered by the Single
       */
      void onError(@NonNull Throwable e);
  }
  